Overview
ISO 12218:1997 - "Graphic technology - Process control - Offset platemaking" is an international standard that establishes unified terminology, test methods and requirements for process control in preparing offset printing formes. Published in 1997 by ISO/TC 130 (Graphic technology), it focuses on contact-based platemaking of pre‑sensitized metal plates (vacuum contact frames, step‑and‑repeat machines and automated contact processors). Optical projection and direct‑writing techniques are excluded, although many principles are applicable by analogy.
Key topics and technical requirements
- Scope and definitions: Standardizes key terms such as exposure, exposure latitude, microline reading, platemaking gradation, screen ruling, contact exposure step, baking and gumming.
- Process control elements:
- Exposure: Role of irradiance and duration; how exposure affects tone value and microline transfer.
- Contact quality: Vacuum drawdown and out‑of‑contact phenomena that reduce transfer fidelity.
- Development: Developer chemistry, temperature, processing speed (development time), and equipment condition (rollers, brushes, finisher).
- Post‑treatment: Baking/post‑exposure to improve durability; gumming to protect plates; correction methods (positive/negative).
- Measurement & test methods:
- Microline targets and readings to define platemaking resolution and reproducible tone‑value shifts.
- Continuous‑tone step wedges to set exposure for negative‑acting plates and to monitor platemaking gradation.
- Guidance on single vs. two‑step exposures for fine screens and for ensuring artefacts (dust, scratches, film edges) are not rendered.
- Quality criteria: Tone‑value change between film and forme, acceptable artefact control, and exposure latitude considerations.
Applications and users
ISO 12218 is practical for:
- Prepress and repro houses controlling offset platemaking workflows
- Plate manufacturers and suppliers of pre‑sensitized plates
- Print production managers and quality control technicians monitoring tone reproduction and run length
- Equipment vendors (vacuum frames, step‑and‑repeat machines, exposure units) integrating process controls
- Standards and compliance teams aligning print production to international best practice
Practical benefits include improved consistency of tone reproduction, predictable run length, reduced plate rejects, and clearer specifications for process monitoring using microline targets and step wedges.
Related standards
- ISO 5-2: Photography - Density measurements - Geometric conditions for transmission density
- ISO 5-3: Photography - Density measurements - Spectral conditions
- ISO 12647-1: Graphic technology - Process control for the manufacture of half‑tone colour separations - Part 1: Parameters and measurement methods
Keywords: ISO 12218, offset platemaking, process control, pre‑sensitized plates, contact exposure, microline target, tone value, platemaking gradation.